When running universal binaries like /bin/bash, Darwin XNU will choose
which architecture of the binary to use based on "binary preferences".
This change sets that to the current platform for aarch64 and x86_64
builds. In addition it now uses posix_spawn instead of the usual
execve. Note, that this does not prevent the other architecture from
being run, just advises which to use.
Unfortunately, posix_spawnattr_setbinpref_np does not appear to be
inherited by child processes in x86_64 Rosetta 2 translations, meaning
that this will not always work as expected.
For example:
{
arm = derivation {
name = "test";
system = "aarch64-darwin";
builder = "/bin/bash";
args = [ "-e" (builtins.toFile "test" ''
set -x
/usr/sbin/sysctl sysctl.proc_translated
/usr/sbin/sysctl sysctl.proc_native
[ "$(/usr/bin/arch)" = arm64 ]
/usr/bin/touch $out
'') ];
};
rosetta = derivation {
name = "test";
system = "x86_64-darwin";
builder = "/bin/bash";
args = [ "-e" (builtins.toFile "test" ''
set -x
/usr/sbin/sysctl sysctl.proc_translated
/usr/sbin/sysctl sysctl.proc_native
[ "$(/usr/bin/arch)" = i386 ]
echo It works!
/usr/bin/touch $out
'') ];
};
}
`arm' fails on x86_64-compiled Nix, but `arm' and `rosetta' succeed on
aarch64-compiled Nix. I suspect there is a way to fix this since:
$ /usr/bin/arch -arch x86_64 /bin/bash \
-c '/usr/bin/arch -arch arm64e /bin/bash -c /usr/bin/arch'
arm64
seems to work correctly. We may need to wait for Apple to update
system_cmds in opensource.apple.com to find out how though.
If the build closure contains some CA derivations, then we can't know
ahead-of-time that we won't build anything as early-cutoff might come-in
at a laster stage
This removes the extra-substituters and extra-sandbox-paths settings
and instead makes every array setting extensible by setting
"extra-<name> = <value>" in the configuration file or passing
"--<name> <value>" on the command line.
This makes it even clearer which of the two hashes was specified in the
nix files. Some may think that "wanted" and "got" is obvious, but:
"got" could mean "got in nix file" and "wanted" could mean "want to see in nix file".
